The Complete Aristotle (eng.)

bed. That is why people say that the figure
is not the nature of a bed, but the wood is-if the bed sprouted not
a bed but wood would come up. But even if the figure is art, then
on the same principle the shape of man is his nature. For man is
born from man.
    We also speak of a thing’s nature as being exhibited in the
process of growth by which its nature is attained. The ‘nature’ in
this sense is not like ‘doctoring’, which leads not to the art of
doctoring but to health. Doctoring must start from the art, not
lead to it. But it is not in this way that nature (in the one
sense) is related to nature (in the other). What grows qua growing
grows from something into something. Into what then does it grow?
Not into that from which it arose but into that to which it tends.
The shape then is nature.
    ‘Shape’ and ‘nature’, it should be added, are in two senses. For
the privation too is in a way form. But whether in unqualified
coming to be there is privation, i.e. a contrary to what comes to
be, we must consider later.
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2
    We have distinguished, then, the different ways in which the
term ‘nature’ is used.
    The next point to consider is how the mathematician differs from
the physicist. Obviously physical bodies contain surfaces and
volumes, lines and points, and these are the subject-matter of
mathematics.
    Further, is astronomy different from physics or a department of
it? It seems absurd that the physicist should be supposed to know
the nature of sun or moon, but not to know any of their essential
attributes, particularly as the writers on physics obviously do
discuss their shape also and whether the earth and the world are
spherical or not.
    Now the mathematician, though he too treats of these things,
nevertheless does not treat of them as the limits of a physical
body; nor does he consider the attributes indicated as the
attributes of such bodies. That is why he separates them; for in
thought they are separable from motion, and it makes no difference,
nor does any falsity result, if they are separated. The holders of
the theory of Forms do the same, though they are not aware of it;
for they separate the objects of physics, which are less separable
than those of mathematics. This becomes plain if one tries to state
in each of the two cases the definitions of the things and of their
attributes. ‘Odd’ and ‘even’, ‘straight’ and ‘curved’, and likewise
‘number’, ‘line’, and ‘figure’, do not involve motion; not so
‘flesh’ and ‘bone’ and ‘man’-these are defined like ‘snub nose’,
not like ‘curved’.
    Similar evidence is supplied by the more physical of the
branches of mathematics, such as optics, harmonics, and astronomy.
These are in a way the converse of geometry. While geometry
investigates physical lines but not qua physical, optics
investigates mathematical lines, but qua physical, not qua
mathematical.
    Since ‘nature’ has two senses, the form and the matter, we must
investigate its objects as we would the essence of snubness. That
is, such things are neither independent of matter nor can be
defined in terms of matter only. Here too indeed one might raise a
difficulty. Since there are two natures, with which is the
physicist concerned? Or should he investigate the combination of
the two? But if the combination of the two, then also each
severally. Does it belong then to the same or to different sciences
to know each severally?
    If we look at the ancients, physics would to be concerned with
the matter. (It was only very slightly that Empedocles and
Democritus touched on the forms and the essence.)
    But if on the other hand art imitates nature, and it is the part
of the same discipline to know the form and the matter up to a
point (e.g. the doctor has a knowledge of health and also of bile
and phlegm, in which health is realized, and the builder both of
the form of the house and of the matter, namely that it is bricks
and beams, and so forth): if this is so, it would be the part of
physics also to know nature in both its senses.
    Again, ‘that for the sake of which’, or the end, belongs to the
same department of knowledge as the means. But the nature is the
end or ‘that for the sake of which’. For if a thing undergoes a
continuous change and there is a stage which is last, this stage is
the end or ‘that for the sake of which’. (That is why the poet was
carried away into making an absurd statement